In equities markets, for trades of a sufficient size it's not possible to place the order all at once. You'll hammer the order book, and take very suboptimal pricing for the latest marginal shares you buy/sell. Therefore you have to split up the order into chunks.
HFT firms will try to detect when equities traders are doing this. e.g. If they see a pattern indicating that chunks of shares are being bought, they will try to buy, too. When the rest of the order comes through, the price will rise and that firm will make money. That's why "front-running" is just a special-case of an algorithm to predict price movements.
I seriously doubt that a HFT fund as large as Rennaissance uses a single strategy, be it satellite images, or front-running or what-have-you.